Why Do Some People Hate the Sound of Chewing? Scientists Might Have the Answer

Some sounds are unbearable for people with misophonia. g-stockstudio/iStock/Thinkstock

It's dinner time with family, and everyone's eating and chatting. Sounds harmless enough, right? But for some, hearing other people's crunching, lip smacking or gulping can cause anger and anxiety. Misophonia is a disorder that often evokes strong, negative feelings in a person to certain sounds — particularly gum chewing, pen clicking, keyboard tapping and rattling pocket change — so much that they have to get away from them.

Recent research published in Current Biology studies the brains of people with misophonia to see how their brains process emotions from certain sounds. Study co-author Dr. Sukhbinder Kumar, research fellow at the Institute of Neuroscience at Newcastle University, and a team of scientists evaluated the data of 42 participants (20 with misophonia, 22 without). People who don't have misophonia can generally tune out everyday sounds that may be a bit bothersome. But for people with misophonia, Kumar says the sensitivity comes from the pattern of the sound, not its volume. The sound aversion is "a sudden realization on the part of the person who has misophonia," he says. "They just can't tolerate the sound and it just goes on and on over time."

While it's not known exactly how many people have the condition, it can be debilitating for the people who do have it. On average, misophonia symptoms start around age 12, but they can appear as early as age 5. "Trigger sounds" often incite rage, and sometimes the sensitivity gets so intense that actions related to specific sounds become disturbing. Imagine a person with misophonia living with a friend, but she doesn't want to talk because she doesn't like the sound of her friend's breathing. "Then it gets a little bit more complicated," Kumar says, "because they also have this feeling that other people are not believing them, so they suffer in silence."

The researchers studied measurements from functional and structural magnetic resonance imaging (fMRI and MRI) and physiological data, observing parts of the brain used for processing perceptions and emotions. Participants heard "trigger sounds," (e.g., eating, breathing, drinking), "unpleasant sounds" (e.g., baby's cry, person's scream) and "neutral sounds" (e.g., busy cafe, rain sound), and both groups rated how annoying the sounds were. Those with misophonia rated how effectively sounds triggered ordinary misophonic reactions. Those without the disorder rated how "antisocial" the sounds would make them, or how much they would dislike being around the noise.

While the misophonic group did experience distress typical of their disorder from the trigger sounds, the unpleasant sounds did not produce the same response. After hearing the trigger sounds, the misophonic group experienced increased heart rates and galvanic skin responses (electric current measured when electrodes are attached to fingertips). According to the authors, these responses are consistent with misophonic tendencies "to escape from the environment of trigger sounds or experience anxiety and anger if unable to escape (fight/flight response)."

The misophonics in the study also exhibited abnormal salience, meaning the trigger sounds stood out more for them. So, parts of the brain involved in detecting salience were more active in misophonics than in nonmisophonics. The trigger sounds targeted the misophonics' anterior insular cortex of the brain, a network that directs our attention toward stimuli that are meaningful to us, and other parts of the brain related to processing and regulating emotion.

Participants also responded to body consciousness questions based on the private body, public body and body competence. Kumar explains that the private body is basically inner perception, like when a person can easily sense her heartbeat. The outer body references one's consciousness about presenting himself to and being perceived by others. Body competence questions asked how participants felt about the strength of their physical characteristics as compared to others'. "We found that people with misophonia had a higher score on the private body and also on the public body, so they were definitely perceiving their body (internally) differently compared to people who don't have misophonia," Kumar says.

The researchers' data doesn't show whether this unusual internal perception is a cause or a result of misophonia. But Kumar is optimistic that further research can be directed to "basically quiet" the brain structures related to the condition. "Just knowing that somebody's researching, [misophonics] will feel a sense of relief," he says.